U.S. patent number 8,043,798 [Application Number 10/644,738] was granted by the patent office on 2011-10-25 for method of forming fine patterns.
This patent grant is currently assigned to Tokyo Ohka Kogyo Co., Ltd.. Invention is credited to Kiyoshi Ishikawa, Tasuku Matsumiya, Tsuyoshi Nakamura, Yoshiki Sugeta, Toshikazu Tachikawa.
United States Patent |
8,043,798 |
Nakamura , et al. |
October 25, 2011 |
Method of forming fine patterns
Abstract
It is disclosed a method of forming fine patterns comprising:
covering a substrate having photoresist patterns thereon made of a
photoresist composition which is sensitive to high energy light
rays with wavelength of 200 nm or shorter or electron beam
radiation, with an over-coating agent for forming fine patterns,
applying heat treatment to cause thermal shrinkage of the
over-coating agent so that the spacing between adjacent photoresist
patterns is lessened by the resulting thermal shrinking action, and
removing the over-coating agent substantially completely. The
present invention provides a method of forming fine patterns
whereby fine patterns having pattern width or diameter of 100 nm or
shorter and being excellent in uniformity (in-plane uniformity),
etc. can be formed by ultrafine processing using high energy light
rays with wavelength of 200 nm or shorter or electron beams.
Inventors: |
Nakamura; Tsuyoshi
(Kanagawa-ken, JP), Matsumiya; Tasuku (Kanagawa-ken,
JP), Ishikawa; Kiyoshi (Kanagawa-ken, JP),
Sugeta; Yoshiki (Kanagawa-ken, JP), Tachikawa;
Toshikazu (Kanagawa-ken, JP) |
Assignee: |
Tokyo Ohka Kogyo Co., Ltd.
(Kanagawa-ken, JP)
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Family
ID: |
32023705 |
Appl.
No.: |
10/644,738 |
Filed: |
August 21, 2003 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040104196 A1 |
Jun 3, 2004 |
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Foreign Application Priority Data
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Aug 21, 2002 [JP] |
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2002-241108 |
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Current U.S.
Class: |
430/324; 430/315;
430/942; 438/760; 430/296; 430/330; 430/322; 427/384; 427/372.2;
427/385.5; 427/271 |
Current CPC
Class: |
H01L
21/0273 (20130101); G03F 7/40 (20130101); C23F
1/02 (20130101); Y10S 430/143 (20130101) |
Current International
Class: |
G03C
5/00 (20060101) |
Field of
Search: |
;430/296,273.1,313,315,322,324,330,942 ;427/271,384,372.2,385.5
;438/760 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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64-023535 |
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01-307228 |
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04-364021 |
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05-166717 |
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05-241348 |
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Sep 1993 |
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07-045510 |
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Feb 1995 |
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JP |
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10-073927 |
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Mar 1998 |
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JP |
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11-153857 |
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Jun 1999 |
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JP |
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11-204399 |
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Jul 1999 |
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JP |
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11-283910 |
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Oct 1999 |
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JP |
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2000-347414 |
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Dec 2000 |
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JP |
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2002-023389 |
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Jan 2002 |
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JP |
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2002-148809 |
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May 2002 |
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JP |
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567533 |
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Dec 2003 |
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TW |
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Other References
"Extended Abstracts" (The 42nd Spring Meeting, 1996); The Japan
Society of Applied Physics and Related Societies, No. 2. cited by
other .
"Extended Abstracts" (The 55th Autumn Meeting, 1994); The Japan
Society of Applied Physics, No. 2. cited by other .
"Proc. SPIE", vol. 4345, pp. 647-654. cited by other .
T. Kijima et al., "Low Temperature Deposition of
Bi.sub.4Ti.sub.3O.sub.12 Thin Films by MOCVD", Functional Devices
Lab. Sharp Corp., with "Concise Explanation of the Relevance with
Respect to Extended Abstracts (The 42nd Spring Meeting, 1995); The
Japan Society of Applied Physics and Related Societies", 29p-D-2.
cited by other .
H. Watanabe et al., "Development of Y1 Materials (Bi Layer
Structured Ferroelectrics) Thin-Film Capacitors (II)", Olympus
Optical Co., Ltd. *Symetrix Co., with "Concise Explanation of the
Relevance with Respect to Extended Abstracts (The 55th Autumn
Meeting, 1994); The Japan Society of Applied Physics", 20p-M-19.
cited by other .
Jun-Sung Chun et al., "Toward 0.1 .mu.m Contact Hole Process by
Using Water Soluble Organic Over-Coating Material (WASOOM); Resist
Flow Technique (III); Study on WASOOM, Top Flare and Etch
Characterization", Advances in Resist Technology and Processing
XVIII, Proceedings of SPIE, vol. 4345 (2001), pp. 647-654. cited by
other .
S. Satoh et al., "Electrical Properties of Bi.sub.4Ti.sub.3O.sub.12
Thin Films by MOCVD", Functional Devices Lab. Sharp Corp., with
"Concise Explanation of the Relevance with Respect to Extended
Abstracts (The 42nd Spring Meeting, 1995); The Japan Society of
Applied Physics and Related Societies", 29p-D-3. cited by
other.
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Primary Examiner: Young; Christopher
Attorney, Agent or Firm: Wenderoth, Lind & Ponack,
L.L.P.
Claims
What is claimed is:
1. A method for forming fine patterns comprising: covering a
substrate having photoresist patterns thereon made of a photoresist
composition which is sensitive to high energy light rays with
wavelength of 200 nm or shorter or electron beam radiation, with an
over-coating agent for forming fine patterns, applying heat
treatment, wherein the heat treatment is performed at a temperature
that does not cause thermal fluidizing of the photoresist patterns
on the substrate, to cause thermal shrinkage of the over-coating
agent so that the spacing between adjacent photoresist patterns is
lessened by the resulting thermal shrinking action, thereby forming
fine patterns having a pattern width or diameter of 100 nm or less,
and removing the over-coating agent substantially completely.
2. The method of forming fine patterns according to claim 1,
wherein the over-coating agent contains a water-soluble
polymer.
3. The method of forming fine patterns according to claim 2,
wherein the water-soluble polymer is at least one member selected
from the group consisting of alkylene glycolic polymers, cellulosic
derivatives, vinyl polymers, acrylic polymers, urea polymers, epoxy
polymers, melamine polymers and amide polymers.
4. The method of forming fine patterns according to claim 1,
wherein the over-coating agent is an aqueous solution having a
solids content of 3 50 mass %.
5. The method for forming fine patterns according to claim 2,
wherein the over-coating agent is an aqueous solution having a
solids content of 3-50 mass%.
6. The method for forming fine patterns according to claim 3,
wherein the over-coating agent is an aqueous solution having a
solids content of 3-50 mass%.
7. The method for forming fine patterns according to claim 2
wherein the water-soluble polymer is a copolymer containing
polyacrylate and polyvinypyrrolidone.
Description
BACKGROUND OF THE INVETNION
1. Field of the Invention
This invention relates to a method of forming fine patterns in the
field of photolithographic technology. More particularly, the
invention relates to a method of forming or defining fine patterns,
such as hole patterns and trench patterns, that can meet today's
requirements for higher packing densities and smaller sizes of
semiconductor devices.
2. Description of the Related Art
In the manufacture of electronic components such as semiconductor
devices and liquid-crystal devices, there is employed the
photolithographic technology which, in order to perform a treatment
such as etching on the substrate, first forms a film (photoresist
layer) over the substrate using a so-called radiation-sensitive
photoresist which is sensitive to activating radiations, then
performs exposure of the film by selective illumination with an
activating radiation, performs development to dissolve away the
photoresist layer selectively to form an image pattern (photoresist
pattern), and forms a variety of patterns including contact
providing patterns such as a hole pattern and a trench pattern
using the photoresist pattern as a protective layer (mask
pattern).
With the recent increase in the need for higher packing densities
and smaller sizes of semiconductor devices, there is a growing
demand for still finer patterns. Following the current tendency,
use is made of short-wavelength radiations such as KrF, ArF and
F.sub.2 excimer laser beams and electron beams (EB) as the
activating light necessary in the formation of mask patterns.
Further, active R&D efforts are being made to find photoresist
materials as mask pattern formers that have physical properties
adapted to those short-wavelength radiations.
In recent years, particular attempts have been vigorously made to
develop ultrafine processing techniques with the use of high-energy
light rays having wavelength of 200 nm or shorter (for example, ArF
or F.sub.2 excimer laser beams) or electron beams and it is an
important problem to be solved to form finer and more precise
photoresist patterns using such photoresist materials adapted to
ultrashort-wavelength radiations.
Existing pattern formation methods with the use of these
photoresist materials adapted to ultrashort-wavelength radiations
are typified by a method which comprises coating such a photoresist
composition adapted to ultrashort-wavelength radiations on a
silicon wafer, drying to form a photoresist layer, irradiating the
photoresist layer selectively with high energy light rays having
wavelength of 200 nm or shorter or electron beams, and then
developing with an alkaline developer to thereby form patterns.
By the existing method as described above, however, it is very
difficult to form fine patterns having pattern width or diameter of
100 nm or less. Even though such fine patterns as having pattern
width or diameter of 100 nm or less can be formed, the obtained
fine patterns frequently suffer from variations in the pattern
dimensions and thus have troubles in uniformity (in-plane
uniformity), etc. Accordingly, these patterns are unsuitable in
practice for the production of semiconductors in most cases.
JP 2001-281886A discloses a method comprising the steps of covering
a surface of a resist pattern with an acidic film made of a resist
pattern size reducing material containing a water-soluble resin,
rendering the surface layer of the resist pattern alkali-soluble,
then removing said surface layer and the acidic film with an
alkaline solution to reduce the feature size of the resist pattern.
JP-2002-184673A discloses a method comprising the steps of forming
a resist pattern on a substrate, then forming a film containing a
water-soluble film forming component on said resist pattern, heat
treating said resist pattern and film, and immersing the assembly
in an aqueous solution of tetramethylammonium hydroxide, thereby
forming a fine-line resist pattern without involving a dry etching
step. However, both methods are simply directed to reducing the
size of resist trace patterns themselves and therefore are totally
different from the present invention in object.
SUMMARY OF THE INVENTION
The present invention, which has been completed under the
above-described circumstances, aims at providing a method of
forming fine patterns whereby fine patterns having pattern width or
diameter of 100 nm or less and being excellent in uniformity
(in-plane uniformity), etc. can be formed by ultrafine processing
using high energy light rays having wavelength of 200 nm or shorter
or electron beams.
In order to attain this object, the present invention provides a
method of forming fine patterns comprising: covering a substrate
having photoresist patterns thereon made of a photoresist
composition which is sensitive to high energy light rays having
wavelength of 200 nm or shorter or electron beam radiation, with an
over-coating agent for forming fine patterns, applying heat
treatment to cause thermal shrinkage of the over-coating agent so
that the spacing between adjacent photoresist patterns is lessened
by the resulting thermal shrinking action, and removing the
over-coating agent substantially completely.
In a preferred embodiment, the heat treatment is performed at a
temperature that does not cause thermal fluidizing of the
photoresist patterns on the substrate.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described below in greater detail.
As a photoresist composition to be used as a photoresist pattern
former in the present invention, use is made of a composition
sensitive to high energy light rays having wavelength of 200 nm or
shorter (ArF and F.sub.2 excimer lasers, etc.) or electron
beams.
As such a photoresist composition, it is preferable to use a
photoresist composition of chemically amplifiable type which
contains an acid generator that generates an acid when exposed to
light or subjected to electron beam photolithography. For example,
citation may be made of a positive-working photoresist of
chemically amplifiable type which contains a polymer having at
least a polyhydroxystyrene unit and a (meth)acrylate unit having a
tertiary-alkyl esterified protecting group and an acid generator,
and a positive-working photoresist of chemically amplifiable type
which contains as its constitutional unit a polymer having a
(meth)acrylate unit having at least one polycyclic hydrocarbon
group in a side chain and showing an elevated solubility in an
alkali under an action of an acid and an acid generator, though it
is not restricted to these compositions.
The substrate having photoresist patterns thereon to be used in the
present invention can be prepared by any methods conventionally
employed in the fabrication of semiconductor devices without
particular limitation. For example, a photoresist composition
sensitive to the high energy light rays having wavelength of 200 nm
or shorter or electron beams as described above is coated on a
substrate such as a silicon wafer with a spinner or the like and
dried to form a photoresist layer, which is then illuminated with
an activating radiation such as excimer laser beams through a
desired mask pattern using a reduction-projection exposure system
or subjected to electron beam photolithography, then heated and
developed with a developer such as an alkaline aqueous solution,
typically a 1 to 10 mass % aqueous tetramethylammonium hydroxide
(TMAH) solution, thereby forming photoresist patterns on the
substrate.
In the conventional methods of forming patterns with the use of
short wavelength activating radiations having wavelength of 200 nm
or shorter or electron beams, patterns having width or diameter of
100 nm or less can be hardly formed in this step. The method
according to the present invention further involves the following
steps. Owing to these subsequent steps, ultrafine patterns of 100
nm or less can be formed or defined by the method of the invention
while sustaining excellent in-plane uniformity.
[a.] Over-Coating Agent Application Step
Next, an over-coating agent is applied to cover entirely the said
substrate having photoresist patterns (mask patterns) thereon.
After applying the over-coating agent, the substrate may optionally
be pre-baked at a temperature of 80 100.degree. C. for 30 90
seconds.
The over-coating agent may be applied by any methods commonly
employed in the conventional heat flow process. Specifically, an
aqueous solution of the over-coating agent for forming fine
patterns is applied to the substrate by any known application
methods including bar coating, roll coating and whirl coating with
a spinner.
The over-coating agent employed in the invention is to cover
entirely the substrate having photoresist patterns (mask patterns)
thereon, including patterns typified by hole patterns or trench
patterns, each of these patterns are defined by spacing between
adjacent photoresist patterns (mask patterns). Upon heating, the
applied film of over-coating agent shrinks to increase the width of
each of the photoresist patterns, thereby narrowing or lessening
adjacent hole patterns or trench patterns as defined by spacing
between the photoresist patterns and, thereafter, the applied film
is removed substantially completely to form or define fine featured
patterns.
The phrase "removing the applied film substantially completely" as
used herein means that after lessening the spacing between adjacent
photoresist patterns by the heat shrinking action of the applied
over-coating agent, said film is removed in such a way that no
significant thickness of the over-coating agent will remain at the
interface with the photoresist patterns. Therefore, the present
invention does not include methods in which a certain thickness of
the over-coating agent is left intact near the interface with the
photoresist pattern so that the feature size of the pattern is
reduced by an amount corresponding to the residual thickness of the
over-coating agent.
In the present invention, the over-coating agent is preferably
employed that contains a water-soluble polymer.
The water-soluble polymer may be any polymer that can dissolve in
water at room temperature and various types may be employed without
particular limitation; preferred examples include acrylic polymers,
vinyl polymers, cellulosic derivatives, alkylene glycol polymers,
urea polymers, melamine polymers, epoxy polymers and amide
polymers.
Exemplary acrylic polymers include polymers and copolymers having
monomeric components, such as acrylic acid, methyl acrylate,
methacrylic acid, methyl methacrylate, N,N-dimethylacrylamide,
N,N-dimethylaminopropylmethacrylamide,
N,N-dimethylaminopropylacrylamide, N-methylacrylamide, diacetone
acrylamide, N,N-dimethylaminoethyl methacrylate,
N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl
acrylate, acryloylmorpholine, etc.
Exemplary vinyl polymers include polymers and copolymers having
monomeric components, such as N-vinylpyrrolidone, vinyl
imidazolidinone, vinyl acetate, etc.
Exemplary cellulosic derivatives include hydroxypropylmethyl
cellulose phthalate, hydroxypropylmethyl cellulose acetate
phthalate, hydroxypropylmethyl cellulose hexahydrophthalate,
hydroxypropylmethyl cellulose acetate succinate,
hydroxypropylmethyl cellulose, hydroxypropyl cellulose,
hydroxyethyl cellulose, cellulose acetate hexahydrophthalate,
carboxymethyl cellulose, ethyl cellulose, methylcellulose, etc.
Exemplary alkylene glycol polymers include addition polymers and
copolymers of ethylene glycol, propylene glycol, etc.
Exemplary urea polymers include those having methylolurea,
dimethylolurea, ethyleneurea, etc. as components.
Exemplary melamine polymers include those having methoxymethylated
melamine, methoxymethylated isobutoxymethylated melamine,
methoxyethylated melamine, etc. as components.
Among epoxy polymers and amide polymers, those which are
water-soluble may also be employed.
It is particularly preferred to employ at least one member selected
from the group consisting of alkylene glycol polymers, cellulosic
derivatives, vinyl polymers and acrylic polymers. Acrylic polymers
are most preferred since they provide ease in pH adjustment.
Copolymers comprising acrylic polymers and water-soluble polymers
other than acrylic polymers are also preferred since during heat
treatment, the efficiency of shrinking the spacing between adjacent
photoresist patterns (mask patterns) can be increased while
maintaining the shape of the photoresist pattern. The water-soluble
polymers can be employed either singly or in combination.
When water-soluble polymers are used as copolymers, the proportions
of the components are not limited to any particular values.
However, if stability over time is important, the proportion of the
acrylic polymer is preferably adjusted to be larger than those of
other building polymers. Other than by using excessive amounts of
the acrylic polymer, better stability over time can also be
obtained by adding acidic compounds such as p-toluenesulfonic acid
and dodecylbenzenesulfonic acid.
The over-coating agent for forming fine patterns may additionally
contain water-soluble amines. Preferred ones include amines having
pKa (acid dissociation constant) values of 7.5 13 in aqueous
solution at 25.degree. C. in view of the prevention of the
generation of impurities and pH adjustment. Specific examples
include the following: alkanolamines, such as monoethanolamine,
diethanolamine, triethanolamine, 2-(2-aminoethoxy)ethanol,
N,N-dimethylethanolamine, N,N-diethylethanolamine,
N,N-dibutylethanolamine, N-methylethanolamine, N-ethylethanolamine,
N-butylethanolamine, N-methyldiethanolamine, monoisopropanolamine,
diisopropanolamine and trilsopropanolamine; polyalkylenepolyamines,
such as diethylenetriamine, triethylenetetramine, propylenediamine,
N,N-diethylethylenediamine, 1,4-butanediamine,
N-ethylethylenediamine, 1,2-propanediamine, 1,3-propanediamine and
1,6-hexanediamine; aliphatic amines, such as triethylamine,
2-ethyl-hexylamine, dioctylamine, tributylamine, tripropylamine,
triallylamine, heptylamine and cyclohexylamine; aromatic amines,
such as benzylamine and diphenylamine; and cyclic amines, such as
piperazine, N-methyl-piperazine and hydroxyethylpiperazine.
Preferred water-soluble amines are those having boiling points of
140.degree. C. (760 mmHg) and above, as exemplified by
monoethanolamine and triethanolamine.
If the water-soluble amine is to be added, it is preferably
incorporated in an amount of about 0.1 30 mass %, more preferably
about 2 15 mass %, of the over-coating agent (in terms of solids
content). If the water-soluble amine is incorporated in an amount
of less than 0.1 mass %, the coating fluid may deteriorate over
time. If the water-soluble amine is incorporated in an amount
exceeding 30 mass %, the photoresist pattern being formed may
deteriorate in shape.
For such purposes as reducing the dimensions of patterns and
controlling the occurrence of defects, the over-coating agent for
forming fine patterns may further optionally contain non-amine
based, water-soluble organic solvents.
As such non-amine based, water-soluble organic solvents, any
non-amine based organic solvents that can mix with water may be
employed and they may be exemplified by the following: sulfoxides,
such as dimethyl sulfoxide; sulfones, such as dimethylsulfone,
diethylsulfone, bis(2-hydroxyethyl)sulfone and
tetramethylenesulfone; amides, such as N,N-dimethylformamide,
N-methylformamide, N,N-dimethylacetamide, N-methylacetamine and
N,N-diethylacetamide; lactams, such as N-methyl-2-pyrrolidone,
N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone,
N-hydroxymethyl-2-pyrrolidone and N-hydroxyethyl-2-pyrrolidone;
imidazolidinones, such as 1,3-dimethyl-2-imidazolidinone,
1,3-diethyl-2-imidazolidinone and
1,3-diisopropyl-2-imidazolidinone; and polyhydric alcohols and
derivatives thereof, such as ethylene glycol, ethylene glycol
monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol
monobuthyl ether, ethylene glycol monomethyl ether acetate,
ethylene glycol monoethyl ether acetate, diethylene glycol,
diethylene glycol monomethyl ether, diethylene glycol monoethyl
ether, diethylene glycol monobuthyl ether, propylene glycol,
propylene glycol monomethyl ether, glycerol, 1,2-butylene glycol,
1,3-butylene glycol and 2,3-butylene glycol. Among those mentioned
above, polyhydric alcohols and their derivatives are preferred for
the purposes of reducing the dimensions of patterns and controlling
the occurrence of defects and glycerol is particularly preferred.
The non-amine based, water-soluble organic solvents may be used
either singly or in combination.
If the non-amine based, water-soluble organic solvent is to be
added, it is preferably incorporated in an amount of about 0.1 30
mass %, more preferably about 0.5 15 mass %, of the water-soluble
polymer. If the non-amine based, water-soluble organic solvent is
incorporated in an amount of less than 0.1 mass %, its defect
reducing effect tends to decrease. Beyond 30 mass %, a mixing layer
is liable to form at the interface with the photoresist
pattern.
In addition, the over-coating agent may optionally contain a
surfactant for attaining special effects such as coating uniformity
and wafer's in-plane uniformity.
The surfactant is preferably employed that, when added to the
water-soluble polymer, exhibits certain characteristics such as
high solubility, non-formation of a suspension and miscibility with
the polymer component. By using surfactants that satisfy these
characteristics, the occurecne of defects can be effectively
controlled that is considered to be pertinent to microforming upon
coating the over-coating agent.
Preferred suitable surfactant in the invention is at least one
member selected among N-alkylpyrrolidones, quaternary ammonium
salts and phosphate esters of polyoxyethylene.
N-alkylpyrrolidones as surfactant are preferably represented by the
following general formula (I):
##STR00001## where R.sub.1 is an alkyl group having at least 6
carbon atoms.
Specific examples of N-alkylpyrrolidones as surfactant include
N-hexyl-2-pyrrolidone, N-heptyl-2-pyrrolidone,
N-octyl-2-pyrrolidone, N-nonyl-2-pyrrolidone,
N-decyl-2-pyrrolidone, N-undecyl-2-pyrrolidone,
N-dodecyl-2-pyrrolidone, N-tridecyl-2-pyrrolidone,
N-tetradecyl-2-pyrrolidone, N-pentadecyl-2-pyrrolidone,
N-hexadecyl-2-pyrrolidone, N-heptadecyl-2-pyrrolidone and
N-octadecyl-2-pyrrolidone. Among these, N-octyl-2-pyrrolidone
("SURFADONE LP 100" of ISP Inc.) is preferably used.
Quaternary ammonium salts as surfactant are preferably represented
by the following general formula (II):
##STR00002## where R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are each
independently an alkyl group or a hydroxyalkyl group (provided that
at least one of them is an alkyl or hydroxyalkyl group having not
less than 6 carbon atoms); X.sup.- is a hydroxide ion or a
halogenide ion.
Specific examples of quaternary ammonium salts as surfactant
include dodecyltrimethylammonium hydroxide,
tridecyltrimethylammonium hydroxide, tetradecyltrimethylammonium
hydroxide, pentadecyltrimethylammonium hydroxide,
hexadecyltrimethylammonium hydroxide, heptadecyltrimethylammonium
hydroxide and octadecyltrimethylammonium hydroxide. Among these,
hexadecyltrimethylammonium hydroxide is preferably used.
Phosphate esters of polyoxyethylene are preferably represented by
the following general formula (III):
##STR00003## where R.sub.6 is an alkyl or alkylaryl group having 1
10 carbon atoms; R.sub.7 is a hydrogen atom or
(CH.sub.2CH.sub.2O)R.sub.6 (where R.sub.6 is as defined above); n
is an integer of 1 20.
To mention specific examples, phosphate esters of polyoxyethylene
that can be used as surfactants are commercially available under
trade names "PLYSURF A212E" and "PLYSURF A210G" from Dai-ichi Kogyo
Seiyaku Co., Ltd.
The amount of the surfactant is preferably about 0.1 10 mass %,
more preferably about 0.2 2 mass %, of the over-coating agent (in
terms of solids content). By adopting the amount as described above
ranges, it may effectively prevent the variations in the percent
shrinkage of patterns, potentially depending on the wafer's
in-plane uniformity which is caused by the deterioration of coating
property, and also prevent the occurrence of defects that are
considered to have cause-and-effect relations with microfoaming on
the applied film that generates as the coating conditions are
worsened.
The over-coating agent used in the invention for forming fine
patterns is preferably used as an aqueous solution at a
concentration of 3 50 mass %, more preferably at 5 30 mass %. If
the concentration of the aqueous solution is less than 3 mass %,
poor coverage of the substrate may result. If the concentration of
the aqueous solution exceeds 50 mass %, there is no appreciable
improvement in the intended effect that justifies the increased
concentration and the solution cannot be handled efficiently.
As already mentioned, the over-coating agent of the invention for
forming fine patterns is usually employed as an aqueous solution
using water as the solvent. A mixed solvent system comprising water
and an alcoholic solvent may also be employed. Exemplary alcoholic
solvents are monohydric alcohols including methyl alcohol, ethyl
alcohol, propyl alcohol and isopropyl alcohol. These alcoholic
solvents are mixed with water in amounts not exceeding about 30
mass %.
[b.] Heat Treatment (Thermal Shrinkage) Step
In the next step, heat treatment is performed to cause thermal
shrinkage of the film of the over-coating agent. Under the
resulting force of thermal shrinkage of the film, the dimensions of
the photoresist pattern in contact with the film will increase by
an amount equivalent to the thermal shrinkage of the film and, as
the result, the photoresist pattern widens and accordingly the
spacing between adjacent photoresist patterns lessens. The spacing
between adjacent photoresist patterns determines the diameter or
width of the pattern elements to be finally obtained, so the
decrease in the spacing between adjacent photoresist patterns
contributes to reducing the diameter of each element of a hole
pattern or the width of each element of a trench pattern,
eventually leading to the definition of a pattern with smaller
feature sizes.
The heating temperature is not limited to any particular value as
long as it is high enough to cause thermal shrinkage of the film of
the over-coating agent and form or define a fine pattern. Heating
is preferably done at a temperature that will not cause thermal
fluidizing of the photoresist pattern. The temperature that will
not cause thermal fluidizing of the photoresist pattern is such a
temperature that when a substrate on which the photoresist pattern
has been formed but no film of the over-coating agent has been
formed is heated, the photoresist pattern will not experience any
dimensional changes. Performing a heat treatment under such
temperature conditions is very effective for various reasons, e.g.
a fine-line pattern of good profile can be formed more efficiently
and the duty ratio in the plane of a wafer, or the dependency on
the spacing between photoresist patterns in the plane of a wafer,
can be reduced. Considering the softening points of a variety of
photoresist compositions employed in current photolithographic
techniques, the preferred heat treatment is usually performed
within a temperature range of about 80 160.degree. C. for 30 90
seconds, provided that the temperature is not high enough to cause
thermal fluidizing of the photoresist.
The thickness of the film of the over-coating agent for the
formation of fine-line patterns is preferably just comparable to
the height of the photoresist pattern or high enough to cover
it.
[d.] Over-Coating Agent Removal Step
In the subsequent step, the remaining film of the over-coating
agent on the patterns is removed by washing with an aqueous
solvent, preferably pure water, for 10 60 seconds. Prior to washing
with water, rinsing may optionally be performed with an aqueous
solution of alkali (e.g. tetramethylammonium hydroxide (TMAH) or
choline). The over-coating agent in the present invention is easy
to remove by washing with water and it can be completely removed
from the substrate and the photoresist pattern.
As a result, each pattern on the substrate has a smaller feature
size because each pattern is defined by the narrowed spacing
between the adjacent widened photoresist patterns.
The fine-line pattern thus formed using the over-coating agent of
the present invention has a pattern size smaller than the
resolution limit attainable by the conventional methods. In
addition, it has a good enough profile and physical properties that
can fully satisfy the characteristics required of semiconductor
devices.
Steps [a.] [c.] may be repeated several times. By repeating steps
[a.] [c.] several times, the photoresist patterns (mask patterns)
can be progressively widened. Since the over-coating agent employed
contains a water-soluble polymer, the over-coating agent can be
completely eliminated in each washing procedure even though
water-washing is performed several times. Consequently, even in the
case of using a substrate having a thick photoresist pattern film
thereon, fineline patterns having favorable profile can be formed
without causing pattern distortion or deformation.
The technical field of the present invention includes the
fabrication of semiconductor devices, etc.
EXAMPLES
The following examples are provided for further illustrating the
present invention but are in no way to be taken as limiting. Unless
otherwise noted, all amounts of ingredients are expressed in mass
%.
Example 1
A copolymer containing polyacrylate (PAA) and polyvinylpyrrolidone
(PVP) [6.36 g; PAA:PVP=2:1 (polymerization ratio)], triethanolamine
(0.57 g) and a polyoxyethyelene phosphate ester surfactant (0.07 g;
"PLYSURF A210G", product of Dai-ichi Kogyo Seiyaku Co, Ltd.) were
dissolved in water (93 g) to prepare an over-coating agent.
Separately, a photoresist being sensitive to electron beams was
prepared by dissolving a copolymer containing polyhydroxystyrene
and tert-butyl acrylate (10 g; 70:30 by polymerization ratio),
perfluorosulfonium triphenylsulfate salt (1.0 g), tributylamine
(0.009 g), salicylic acid (0.005 g) and a surfactant (0.006 g;
"XR-104", product of Dainippon Ink & Chemicals Inc.) in ethyl
lactate (89 g).
The photoresist was whirl coated on a substrate and baked at
140.degree. C. for 90 seconds to form a photoresist layer in a
thickness of 0.40 .mu.m.
Next, the photoresist layer was subjected to an electron beam
photolithography using an exposure unit "HL-800D" (product of
Hitachi Instruments Service Co., Ltd.), heated at 130.degree. C.
for 90 seconds and developed with a 2.38 mass % aqueous solution of
TMAH (tetramethylammonium hydroxide) to thereby form photoresist
patterns. By forming the photoresist patterns, hole patterns of 100
nm in hole diameter were defined.
Next, the above-described over-coating agent was applied onto the
substrate including hole patterns and subjected to heat treatment
at 120.degree. C. for 60 seconds, thereby reducing the each size of
the hole patterns. Subsequently, the substrate was brought into
contact with pure water at 23.degree. C. to remove the over-coating
agent. The each diameter of the hole patterns was reduced to 65 nm.
None of the fine patterns showed any variations in pattern
dimensions of 6.5 nm (i.e., .+-.10% of the diameter of the fine
patterns) or more, and indicates the excellent in-plane
uniformity.
Comparative Example 1
Using the photoresist prepared in EXAMPLE 1, the procedure of
forming photoresist patterns as described in EXAMPLE 1 was
followed, but omitting the subsequent treatment of forming fine
patterns with the use of the over-coating agent. Thus, hole
patterns of 100 nm in diameter were defined. In this case,
variations in the pattern dimensions exceeding 10 nm (i.e., .+-.10%
of the pattern size) arose in the plane, thus resulting in a fear
of seriously lowering the yield.
As discussed above in detail, the present invention provides a
method whereby fine patterns having pattern width or diameter of
100 nm or less and being excellent in uniformity (in-plane
uniformity), etc. can be formed by ultrafine processing using high
energy light rays with wavelength of 200 nm or shorter or electron
beams.
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